1. Field of the Invention
The present invention relates to a bonding method and bonding configuration for bonding a connecting member or a mounting stay, which is used in a pressure accumulation fuel injection system, to a surface of a metal base material through welding. The present invention also relates to a common rail mounted on a common rail fuel injection system, which injects fuel into an internal combustion engine, for accumulating high-pressure fuel. Specifically, the present invention relates to a bonded common rail that is formed by welding multiple parts.
2. Description of Related Art
When a pipe connector is bonded to a common rail of a pressure accumulation fuel injection system of an internal combustion engine, strength and positional accuracy of the bonded portion are required.
International Publication No. 01/66934 (WO '934) discloses a convex positioning portion on an outer peripheral surface of the common rail. The connector is fit to the positioning portion to ensure positional accuracy. Thus, WO '934 performs the welding process to ensure bonding strength.
In a resistance welding process, a current is conducted through contacting points of the common rail and the connector to be bonded, and the common rail and the connector are welded with the use of heat that is generated at the contacting points by electric resistance at the contacting points. Therefore, if the current flows through a positioning portion, which is not the contacting points, the density of the current flowing through the contacting points is reduced, and the bonding strength becomes insufficient. Therefore, WO '934 discloses interposing an insulating ring between the positioning portion and the connector to prevent the current from flowing through the positioning portion during the resistance welding process.
However, since the technology described in WO '934 uses the insulator ring, which does not provide any improvement in performance of the product, cost is increased unnecessarily.
In a pressure accumulation fuel injection system, the common rail is mounted to the internal combustion engine through a mounting stay. Therefore, positional accuracy of the mounting stay with respect to the common rail is important. If the bonding position of the mounting stay is deviated when the mounting stay is bonded to the common rail, it affects the positional accuracy of the connector with respect to the common rail. Usually, the positional accuracy of the mounting stay with respect to the common rail is ensured by performing jig adjustment.
A method that ensures the positional accuracy of the mounting stay with respect to the common rail by a jig adjustment cannot absorb a dimensional error of the common rail or the mounting stay. Therefore, if an error occurs, e.g., in length of the common rail or the external diameter of the mounting stay, the positional accuracy of the mounting stay with respect to the common rail is deteriorated. Also, if thermal expansion of the common rail is caused by heat generation when the resistance welding process is performed, the positional accuracy of the mounting stay is deteriorated by the influence of the thermal expansion.
A forged common rail is manufactured by forming a rail main body that accumulates high-pressure fuel and joints for pipe connection in a single piece through a forging process.
A bonded common rail is described in JP-A-2005-9672. Multiple parts of the bonded common rail are produced separately and are bonded with each other through a welding process. The bonded common rail can improve productivity and reduce cost compared to a forged common rail. Joint type common rails (for example, as shown in FIGS. 33A to 34C) and sleeve type common rails (for example, as shown in FIGS. 35A to 35C) are examples of bonded common rails.
As shown in FIG. 33A, a rail main body 70, a cylindrical connector 72, and a joint 23 for pipe connection of the joint type common rail are manufactured separately, first. A first flat surface 74, to which the connector 72 is to be bonded, is formed on an upper surface of the rail body 70 in FIG. 33A along a longitudinal direction. Then, the rail main body 70 and the connector 72 are bonded through electric resistance welding process, and the joint 23 is fastened to the connector 72. Thus, the joint type common rail is manufactured as shown in FIG. 33B. A conical portion 33 on a tip end of each one of pipes 56, 57 is connected to the joint 23 by threading a pipe fastening nut 35 to the joint 23 as shown in FIG. 33C. The joint 23 is made of a metal material of iron family. A joint passage 28 is formed at the axial center of the joint 23. The joint passage 28 communicates an inside-outside communication hole 76 with an inner passage of each one of the pipes 56, 57.
A main body side male thread 29 is formed on an end of the joint 23. The main body side male thread 29 is screwed into a connector thread 77. A pipe side male thread 30 is formed on the other end of the joint 23. The pipe side male thread 30 is used to connect the pipe 56, 57.
A second flat surface 31 is formed on an end surface of the joint 23, on which the main body side male thread 29 is formed. The second flat surface 31 coincides with the first flat surface 74 of the rail main body 70. More specifically, the second flat surface 31 is formed on the end surface of the main body side male thread 29 to surround the joint passage 28.
The main body side male thread 29 is screwed into the connector thread 77, and the tip end of the main body side male thread 29 is pushed deeply into the connector 72. Thus, the joint passage 28 opening in the second flat surface 31 communicates with the inside-outside communication hole 76 opening in the first flat surface 74, and the second flat surface 31 around the joint passage 28 is pressed against the first flat surface 74 around the inside-outside communication hole 76 to form a main body sealing surface (oil-tight surface) 32.
A pressure receiving seat surface 34 in a conically tapered shape is formed on the end surface of the joint 23 on a side where the pipe side male thread 30 is formed. The conical portion 33 formed on a tip end of each one of the pipes 56, 57 is inserted into the pressure receiving seat surface 34. The joint passage 28 opens in the bottom of the pressure receiving seat surface 34.
A nut thread (female thread) 36 is formed on an inner peripheral surface of the pipe fastening nut 35, which is fit to each one of the pipes 56, 57. The pipe side male thread 30 is threaded with the nut thread 36. The pipe fastening nut 35 is threaded with the pipe side male thread 30 of the joint 23 in a state in which the pipe fastening nut 35 strikes the step formed on the backside of the conical portion 33 of each one of the pipes 56, 57. By threading the pipe fastening nut 35 to the pipe side male thread 30, the conical portion 33 of each one of the pipes 56, 57 is pressed against the pressure receiving seat surface 34 to form a pipe sealing surface (oil-tight surface) 37.
As shown in FIG. 34A, a rail main body 70, a cylindrical connector 82, and a joint 23 for pipe connection of the joint type common rail are manufactured separately, first. A first flat surface 74, to which the connector 82 is to be bonded, is formed on an upper surface of the rail body 70 in FIG. 34A along a longitudinal direction. Then, the rail main body 70 and the connector 82 are bonded through laser welding process, and the joint 23 is fastened to the connector 82. Thus, the joint type common rail is manufactured as shown in FIG. 34B.
The main body side male thread 29 is screwed into a connector thread 87 of the connector 82, and the tip end of the main body side male thread 29 is pushed deeply into the connector 82. Thus, the joint passage 28 opening in the second flat surface 31 communicates with the inside-outside communication hole 76 opening in the first flat surface 74, and the second flat surface 31 around the joint passage 28 is pressed against the first flat surface 74 around the inside-outside communication hole 76 to form a main body sealing surface (oil-tight surface) 32.
A rail main body 80 and a cylindrical connector 92 of the sleeve type common rail are manufactured separately as shown in FIG. 35A. Then, the rail main body 80 and the connector 92 are bonded through electric resistance welding process (or laser welding process). Thus, as shown in FIG. 35B, the sleeve type common rail is manufactured. A conical portion 133 on a tip end of each one of pipes 66, 67 and a part of a sleeve 143 are inserted into the connector 92, and a pipe fastening nut 135 is threaded to the connector 92. Thus, the conical portion 133 on the tip end of each one of the pipes 66, 67 is connected directly to a pressure receiving seat surface 134 of the rail main body 80. A first flat surface 84 is formed on an upper surface of the rail main body 80 in FIG. 35A. An inside-outside communication hole 86 opens in the bottom of the pressure receiving seat surface 134. A nut thread 136 is formed on an inner peripheral surface of the pipe fastening nut 135. The connector 92 is formed with a connector thread 127. The conical portion 133 and the pressure receiving seat surface 134 form a main body sealing surface (oil-tight surface) 137.
Since the forged common rail is manufactured in a single piece through a forging process, shape accuracy of respective parts can be improved. Since the bonded common rail is manufactured by manufacturing respective parts (for example, the rail main body 70, 80 and the connector 72, 82, 92) separately and by welding the parts, it has been difficult to attain the same shape accuracy as that of the forged common rail.
Specifically, the part bonded to a flat surface is affected by shape accuracy of a welding jig. Therefore, it has been difficult to manufacture the bonded common rail with high accuracy.